Devices and method for augmenting a vertebral disc

ABSTRACT

A vertebral disc prosthesis, a method of implanting a prosthesis and a deployment device is provided. The prosthesis may be implanted into the interior region of the vertebral disc so as to displace existing vertebral tissue, such as NP. The size or amount of the prosthesis inserted into the interior region of the vertebral disc may be a characteristic of the disc or the prosthesis. For example, the amount or size of prosthesis inserted into the disc may be dependent upon restoring the functionality of the disc (e.g., the ability of the disc to transfer nutrients or otherwise survive, the ability of the disc to carry the required loads and absorb stress or the reduction of pain). Restoring disc function may be determined by the resulting disc height desired, the resulting disc pressure desired or the resulting disc volume desired. The prosthesis may be sized or positioned within the interior of the vertebral disc such that it is spaced from at least one of the end plates of the vertebral disc. The prosthesis may be formed of a material having a compression strength that is less than 4 mn/m 2 . A deployment device may be used to facilitate placement of the prosthesis within the vertebral disc. The prosthesis may include a grouping of multiple components that can be deployed as group.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication Ser. Nos. 60/439,261, filed on Jan. 10, 2003; 60/438,022,filed on Jan. 3, 2003; and 60/417,219, filed Oct. 9, 2002.

[0002] This application is also a continuation-in-part of U.S.application Ser. No. 10/055,504 filed on Oct. 25, 2001, now pending,which is a continuation-in-part of U.S. application Ser. No. 09/696,636filed on Oct. 25, 2000, now U.S. Pat. No. 6,508,839, which is acontinuation-in-part of U.S. application Ser. No. 09/642,450 filed onAug. 18, 2000, now U.S. Pat. No. 6,482,235, which is acontinuation-in-part of U.S. application Ser. No. 09/608,797 filed onJun. 30, 2000, now U.S. Pat. No. 6,425,919.

[0003] Application Ser. No. 10/055,504 claims the benefit of U.S.Provisional Application Ser. No. 60/311,586 filed on Aug. 10, 2001.Application Ser. Nos. 09/642,450 and 09/608,797 each claim the benefitof U.S. Provisional Application Ser. Nos. 60/172,996, filed on Dec. 19,1999; 60/161,085, filed on Oct. 25, 1999; and 60/149,490 filed Aug. 18,1999.

[0004] Each of these applications is hereby incorporated herein byreference in their entirety.

FIELD OF INVENTION

[0005] The present inventions relate generally to treatment of vertebraldiscs in the lumbar, cervical, or thoracic spine.

DISCUSSION OF RELATED ART

[0006] The disc performs the role of absorbing mechanical loads whileallowing for constrained flexibility of the spine. The vertebral tissueforming the disc includes a soft, central nucleus pulposus (NP)surrounded by a tough, woven annulus fibrosis (AF) and superior andinferior endplates. Herniation is a result of a weakening in the AF.Symptomatic herniations occur when weakness in the AF allows the NP tobulge or leak, for example, toward the spinal cord and major nerveroots. The most common resulting symptoms are pain radiating along anerve and low back pain, both of which can be crippling for the patient.

[0007] Discectomy has been the most common surgical procedure fortreating vertebral disc herniation. This procedure involves removal ofdisc materials impinging on the nerve roots or spinal cord external tothe disc. Depending on the surgeon's preference, varying amounts of NPmay also be removed from within the disc space either through theherniation site or through an incision in the AF. This removal of extraNP is commonly done to minimize the risk of recurrent herniation.

SUMMARY OF THE INVENTION

[0008] In one embodiment, a vertebral disc prosthesis is provided. Theprosthesis includes a mass of material that is adapted to be insertedinto the interior region of the vertebral disc.

[0009] The mass of material has a compressive strength of less than 4MN/m². to In another embodiment, a prosthesis for implantation into aninterior region of a vertebral disc is provided. The vertebral discincludes first and second endplates. The prosthesis includes a mass ofmaterial that is adapted for insertion into the interior region of thevertebral disc so as to displace existing vertebral tissue. The mass ofmaterial is sized so as to be spaced from both the first and secondendplates when implanted into the interior region of the vertebral discsuch that the mass of material is surrounded with nucleus pulposuswithin the interior region of the vertebral disc when implanted therein.

[0010] In yet another embodiment, a prosthesis for implantation into aninterior region of a vertebral disc is provided. The prosthesis includesan isotropic mass of biocompatible hydrogel having a compressivestrength of less than 4 MN/in² and a volume between a range ofapproximately 0.1 ml and approximately 6.0 ml.

[0011] In another embodiment, a method of inplanting a prosthesismaterial into an interior region of a vertebral disc is disclosed. Themethod includes locating an access site on the disc; inserting, throughan opening of the disc at the access site, the prosthesis material intothe interior region of the vertebral disc; and monitoring at least oneof: a) one or more characteristics of the vertebral disc, and b) one ormore characteristics of the prosthesis material.

[0012] In still another embodiment, a method of restoring function of avertebral disc is disclosed. The method includes locating an access siteon the disc; and inserting, through an opening of the disc at the accesssite, a prosthesis material into an interior region of the vertebraldisc without removing a substantial amount of nucleus pulposus from theinterior region so as to augment existing nucleus pulposus.

[0013] In still another embodiment, a method of implanting a prosthesismaterial into an interior region of a vertebral disc is disclosed. Thevertebral disc has first and second endplates. The method includeslocating an access site on the disc; inserting, through an opening ofthe disc at the access site, the prosthesis material into the interiorregion of the vertebral disc without removing a substantial amount ofnucleus pulposus; spacing the prosthesis material from the endplates ofthe vertebral disc such that the nucleus pulposus substantiallysurrounds the prosthesis material. The method also includes monitoringat least one of: a) one or more characteristics of the vertebral disc,and b) one or more characteristics of the prosthesis material.

[0014] In yet another embodiment, a method of increasing a height of avertebral disc is disclosed. The method includes locating an access siteon the disc; and inserting, through an to opening of the disc at theaccess site, an amount of prosthesis material into an interior region ofthe vertebral disc without removing a substantial amount of nucleuspulposus from the interior region so as to augment existing nucleuspulposus. The method also includes monitoring the disc height todetermine whether a desired disc height is achieved.

[0015] In another embodiment, a method of increasing a intradiscalpressure of a vertebral disc is disclosed. The method includes locatingan access site on the disc; and inserting, through an opening of thedisc at the access site, an amount of prosthesis material into aninterior region of the vertebral disc without removing a substantialamount of nucleus pulposus from the interior region so as to augmentexisting nucleus pulposus. The method also includes monitoring theintradiscal pressure to determine whether a desired intradiscal pressureis achieved.

[0016] In still another embodiment, a device for delivering a prosthesismaterial to an interior region of a vertebral disc is provided. Thedevice includes a body having a proximal end and a distal end and aholder region disposed adjacent the distal end of the body. The holderregion being adapted to hold the prosthesis material prior to deliveryinto the interior region of the vertebral disc. The device furtherincludes a plunger disposed within the body. The plunger and body areadapted to move relative to each other to dispense the prosthesismaterial. A stop is disposed on the body. The stop is adapted to allowpositioning of the body relative to the interior region of the vertebralbody such that the prosthesis material can be dispensed within theinterior region of the vertebral body at a desired location.

[0017] In another embodiment, a device for delivering a prosthesismaterial to an interior region of a vertebral disc is disclosed. Thedevice includes a body having a proximal end and a flexible distal end.The body defines a longitudinal axis. The flexible distal end is adaptedto articulate relative to the axis. A holder region is disposed adjacentthe distal end of the body. The holder region is adapted to hold theprosthesis material prior to delivery into the interior region of thevertebral disc. A plunger is disposed within the body. The plunger andbody are adapted to move relative to each other to dispense theprosthesis.

[0018] In another embodiment, a device for delivering a prosthesismaterial to an interior region of a vertebral disc is disclosed. Thedevice includes a body having a proximal end and a distal end. The bodyis formed as a hollow sleeve. A holder region is disposed adjacent thedistal end of the body. The holder region is adapted to hold theprosthesis material prior to delivery into the interior region of thevertebral disc. A plunger is axially disposed within the sleeve. Thesleeve is adapted to be retracted relative to the plunger to dislodgethe prosthesis material from the holder region upon retraction of thesleeve.

[0019] In yet another embodiment, a device for delivering a prosthesismaterial to an interior region of a vertebral disc is disclosed. Thedevice includes a body having a proximal end and a distal end. A holderregion is disposed adjacent the distal end. The holder region is adaptedto hold the prosthesis material prior to delivery into the interiorregion of the vertebral disc. The holder region includes a plurality ofopenings, with each opening adapted to allow prosthesis material to bedispensed from within the holder region. A plunger is disposed withinthe body. The plunger and body are adapted to move relative to eachother to dispense the prosthesis material.

[0020] In still another embodiment, a device for delivering a prosthesismaterial to an interior region of a vertebral disc is disclosed. Thedevice includes a body having a proximal end and a distal end. A holderregion is disposed adjacent the distal end of the body. The holderregion is adapted to hold the prosthesis material prior to delivery intothe interior region of the vertebral disc. A plunger is disposed withinthe body. The plunger and body are adapted to move relative to eachother to dispense the prosthesis material. A gauge cooperates with thedevice and is adapted to measure the insertion force of the prosthesismaterial into the inner region of the vertebral disc.

[0021] In another embodiment, a method for delivering a prosthesismaterial into an interior region of a vertebral disc is disclosed. Themethod includes providing a delivery device having a body having aproximal end and a distal end and a holder region disposed adjacent thedistal end. The holder region is adapted to hold the prosthesis materialprior to delivery into the interior region of the vertebral disc. Thedelivery device further including a plunger cooperating with the body.The method further includes loading the holder region with theprosthesis material, advancing at least a portion of the device to adesired location within the vertebral disc, and moving the plungerrelative to the body to dislodge the prosthesis material from thedevice.

[0022] In still another embodiment, a kit of parts for use in augmentingvertebral tissue is disclosed. The kit includes a prosthesis accordingto any of the embodiments described herein; and a device for insertingthe prosthesis into the interior region of the vertebral disc.

[0023] In yet another embodiment, a kit of parts for use in augmentingvertebral tissue is disclosed, the kit includes a prosthesis adapted forinsertion into the vertebral disc; a delivery device for inserting theprosthesis into the interior region of the vertebral disc; andinstructions for inserting the prosthesis, the instructions comprisinginstructions for inserting the prosthesis material into an interiorregion of the vertebral disc without removing a substantial amount ofnucleus pulposus from the disc.

[0024] In still another embodiment, a kit of parts for use in augmentingvertebral tissue is disclosed. The kit includes a prosthesis adapted forinsertion into the vertebral disc; a delivery device for inserting theprosthesis into the interior region of the vertebral disc; andinstructions for inserting the prosthesis. The instructions comprisingthe any of the methods disclosed herein.

[0025] In still another embodiment, a kit of parts for use in augmentingvertebral tissue is disclosed. The kit includes a prosthesis adapted forinsertion into the vertebral disc; and a delivery device according toany of the embodiments described herein.

[0026] In another embodiment, a vertebral disc prosthesis for displacingnucleus, annulus, or vertebral body endplate tissue of a vertebral discis disclosed. The prosthesis includes a grouping of at least twodiscrete components. The grouping is constructed and configured to beinserted together as a group into the interior region of a vertebraldisc to displace at least a portion of the nucleus, annulus, orvertebral body endplate tissue.

[0027] In yet another embodiment, a method of restoring function of anvertebral disc is disclosed. The vertebral disc has vertebral disctissue comprising a nucleus, an annulus, and vertebral body endplatetissue. The method includes locating an access site on the vertebraldisc; and inserting, at one time, a prosthesis comprising a grouping ofat least two discrete components through the access site and into aninterior region of the vertebral disc to displace at least a portion ofthe vertebral disc tissue without removing a substantial amount ofnucleus tissue.

[0028] Various embodiments of the present invention provide certainadvantages and overcome certain drawbacks of prior prostheses.Embodiments of the invention may not share the same advantages, andthose that do may not share them under all circumstances. Furtherfeatures and advantages of the present invention, as well as thestructure of various illustrative embodiments, are described in detailbelow with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Various embodiments of the invention will now be described, byway of example, with reference to the accompanying drawings, in which:

[0030]FIG. 1A is a cross-sectional view of a portion of a functionalspine unit, in which part of a vertebra and vertebral disc are depicted;

[0031]FIG. 1B is a side view of a portion of the functional spine unitshown in FIG. 1A, in which two lumbar vertebrae and the vertebral discare visible, and wherein a prosthesis of the present invention is shown;

[0032]FIG. 2 is a side view of the functional spine unit shown in FIG.1A, wherein a prosthesis according to another aspect to the invention isshown;

[0033]FIGS. 3A and 3B are views of the vertebral disc, wherein aprosthesis according to yet another aspect of the invention is shown;

[0034]FIG. 4 is a cross-sectional view of a portion of a functionalspine unit, wherein a prosthesis according to still another aspect ofthe invention is shown;

[0035]FIG. 5 is a cross-sectional view of a portion of a functionalspine unit, wherein a prosthesis according to yet another aspect of theinvention is shown;

[0036]FIGS. 6A and 6B are views of a portion of a functional spine unit,wherein a prosthesis according to yet another aspect of the invention isshown;

[0037]FIGS. 7A and 7B are views of a functional spine unit, wherein aprosthesis according to yet another aspect of the invention is shown;

[0038]FIG. 8 is a cross-sectional view of a portion of a functionalspine unit, wherein a prosthesis according to still another aspect ofthe invention is shown;

[0039]FIG. 9 is a cross-sectional view of a portion of a functionalspine unit, wherein a prosthesis according to still another aspect ofthe invention is shown;

[0040]FIG. 10 is a cross-sectional view of a portion of a functionalspine unit showing the prosthesis cooperating with a barrier accordingto another aspect of the invention;

[0041]FIG. 11 is diagrammatic representation of the vertebral discshowing a barrier positioned within the interior region of the disc;

[0042]FIGS. 12A through 12C are cross-sectional representations of adeployment device used to deploy the prosthesis according to one aspectof the invention;

[0043]FIG. 13 is an alternative embodiment of the deployment deviceshown in FIGS. 12A-12C;

[0044] FIGS. 14A-14D show alternative embodiments of a portion of thedeployment device encircled by line 14 of FIG. 12A;

[0045]FIG. 15 is a cross-sectional representation of a portion of thedeployment device showing yet another alternative embodiment to theinvention;

[0046]FIGS. 16 and 17 are cross-sectional views of a portion of thedeployment device according to alternative embodiments of the invention;

[0047] FIGS. 18A-18C are cross-sectional representations of deploymentdevice according to an alternative embodiment of the invention;

[0048]FIG. 19 is a diagrammatic prospective view of a portion of thedeployment device shown in FIGS. 18A-18C;

[0049]FIG. 20A is a diagrammatic cross-section representation of aportion of an alternative embodiment of the deployment device;

[0050]FIG. 20B is a diagrammatic cross-section representation of aportion of another alternative embodiment of the deployment device;

[0051]FIGS. 21A and 21B are diagrammatic cross-sectional representationsof alternative embodiments of the deployment device;

[0052]FIG. 22 is a diagrammatic cross-sectional representation of yetanother alternative embodiment of the deployment device;

[0053]FIGS. 23A through 23C are cross-sectional representations of adeployment device used to deploy the prosthesis according to one aspectof the invention; and

[0054]FIGS. 24A through 24C are cross-sectional representations of adeployment device used to deploy the prosthesis according to one aspectof the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0055] Loss of vertebral disc tissue, such as NP, deflates the disc,causing a decrease in disc height. Significant decreases in disc heighthave been noted in up to 98% of operated patients. Loss of disc heightincreases loading on the facet joints, which may result in deteriorationof facet cartilage and ultimately osteoarthritis and pain. As the jointspace decreases, the neural foramina formed by the inferior and superiorvertebral pedicles also close down which could lead to foraminalstenosis, pinching of the traversing nerve root, and recurring radicularpain. Loss of NP also increases loading on the remaining AF, and canproduce pain. Finally, loss of NP results in greater bulging of the AFunder load, which may result in renewed impingement by the AF on nervestructures posterior to the disc. Removal of NP may also be detrimentalto the clinical outcome of disc repair.

[0056] Applicants own U.S. Pat. Nos. 6,425,919; 6,482,235; 6,508,839 andPublished U.S. patent application Ser. No. 2002/0151979, each of whichis hereby incorporated by reference in its entirety, and discloses,inter alia, methods and devices directed to reinforcing and augmentingthe annulus of an vertebral disc. As will be explained, such devices andmethods can be used with the inventions described herein.

[0057] In various aspects of the invention, a vertebral disc prosthesis,a method of implanting a prosthesis and a deployment device aredisclosed.

[0058] In one aspect of the invention, the prosthesis is implanted intothe interior region of the vertebral disc to move or displace, but notreplace, the autologous or existing NP, AF or one or both endplates. Thetissues of the AF, NP or endplate(s) is therefore displaced relative tothe amount of prosthesis added. While a deminimis amount of vertebraltissue may be removed, a substantial amount of material (such as the NP)is not removed. In this manner, as will be explained, a more naturalbiomechanical state is achieved and functionality of the disc isretained. Prior methods include removal of some of the vertebral tissue,such as a substantial amount or all of the NP, which may disrupt thebiomechanical function of the disc as well as the ability of the disc tosurvive. According to aspects of the present invention, the size oramount of prosthesis inserted into the interior region of the vertebraldisc is a function of certain characteristics of the disc or theprosthesis. For example, the amount or size of prosthesis inserted intothe disc may be dependent upon restoring the functionality of the disc(e.g., the ability of the disc to transfer nutrients or otherwisesurvive, the ability of the disc to carry the required loads and absorbstress or the reduction of pain). Restoring disc function may bedetermined by the resulting disc height desired, the resulting discpressure desired or the resulting disc volume desired. The prosthesismay also be sized or positioned within the interior region of thevertebral disc such that it is spaced from at least one of the endplatesof the vertebral disc. In this manner, the natural ability for the discto transfer nutrients to and from the AF and the endplates by allowing amore natural diffusion of enriched fluids may be achieved. As will beexplained in more detail below, in another aspect, the prosthesis may beformed of any suitable material as the present invention is not limitedin this respect. In one embodiment, however, the prosthesis is formed ofa material having a compression strength that is less than 4 MN/m². Forexample, a hydrogel material may be employed. As will be apparent to oneof skill in the art, the hydrogel may be processed with suitablecross-linking agents or formed with a desired degree of cross-linking,or processed using a suitable freeze/thaw cycle to produce a materialwith the desired compressive strength.

[0059] In yet another aspect of the invention, to facilitate placementof the prosthesis within the vertebral disc, a deployment device isdisclosed. The deployment device may include a number of features that,either singularly or in any suitable combination, enhance placement ofthe prosthesis. The deployment device may include at least one or moreof the following: a depth stop to facilitate placement of the prosthesisrelative to an anatomical feature; a curved or atriculatable end tofacilitate inserting the prosthesis in a desired location; a pluralityof openings formed on the insertion end of the device to allow a moreuniform distribution of the prosthesis material within the disc; and agauge to allow a determination as to whether a sufficient amount of theprosthesis material is placed within the vertebral disc. Further, ratherthan forcing the prosthesis into the interior region, the deploymentdevice may be constructed such that upon retraction, the prosthesis isleft behind.

[0060] The prosthesis may be shaped and sized or otherwise configured tobe inserted through an opening in the vertebral disc. Such an openingmay be a defect in the AF such as a hernia site, or may be a surgicallycreated opening. The prosthesis may also be positioned within theinterior region of the vertebral disc so as to be spaced away from theaccess opening and therefore reduce the likelihood that the prosthesismay be dispensed or extruded therefrom. Surgical approaches includingtranspsoas, presacral, transsacral, tranpedicular, translaminar, oranteriorly through the abdomen, may be used. The access opening can belocated anywhere along the surface of the AF or even through thevertebral endplates.

[0061] Turning now to the figures, illustrative embodiments of theprosthesis and deployment device, and illustrative methods for insertingthe prosthesis will now be described. Although certain features will bedescribed with reference to a specific embodiment, the present inventionis not limited in this respect, as any of the features described herein,and other suitable features, may be employed singularly or any suitablecombination to form any suitable embodiment.

[0062] A functional spine unit includes the bony structures of twoadjacent vertebrae (or vertebral bodies), the soft tissue (annulusfibrosis (AF), nucleus pulposus (NP), and endplates) of the vertebraldisc, and the ligaments, musculature and connective tissue connected tothe vertebrae. The vertebral disc is substantially situated in thevertebral space formed between the adjacent vertebrae.

[0063]FIGS. 1A and 1B show the general anatomy of a functional spineunit 10. As used herein, the terms ‘anterior’ and ‘posterior’,‘superior’ and ‘inferior’ are defined by their standard usage inanatomy, i.e., anterior is a direction toward the front (ventral) sideof the body or organ, posterior is a direction toward the back (dorsal)side of the body or organ; superior is upward (toward the head) andinferior is lower (toward the feet).

[0064]FIG. 1A is a cross-sectional view of a vertebral body with thevertebral disc 15 superior to the vertebral body. Anterior (A) andposterior (P) sides of the functional spine unit are also shown. Thevertebral disc 15 contains an annulus fibrosis (AF) 17 surrounding acentral nucleus pulposus (NP) 20. Also shown in this figure are the left22 and right 22′ transverse spinous processes and the posterior spinousprocess 24.

[0065]FIG. 1B is a side view of two adjacent vertebral bodies 28(superior) and 30 (inferior). Vertebral disc space 32 is formed betweenthe two vertebral bodies and contains vertebral disc 15, which supportsand cushions the vertebral bodies and permits movement of the twovertebral bodies with respect to each other and other adjacentfunctional spine units.

[0066] Vertebral disc 15 includes the AF 17, which normally surroundsand constrains the NP 20 to be wholly within the borders of thevertebral disc space. The vertebral disc 15 also includes superiorendplate 34 and inferior endplate 36 that cooperate with the AF 17 tocontain the NP 20 within the borders of the vertebral disc space. Thevertebral bodies also include facet joints 38 and the superior 40 andinferior 42′ pedicle that form the neural foramen 44. Loss of discheight (H) occurs when the superior vertebral body 28 moves inferiorlyrelative to the inferior vertebral body 30.

[0067] In one illustrative embodiment, the prosthesis 50 is insertedinto the interior region 52 of the vertebral disc 15 so as to displaceexisting NP, AF or the endplate(s). That is, existing tissue, such as NPmaterial, is not removed during insertion of the prosthesis, as is donein prior methods. As discussed above, prior methods include removal ofsome or all of the NP from the vertebral disc, which may disrupt thebiomechanical function of the disc as well as the ability of the disc tosurvive. Also, prior prostheses were sized to merely fill the surgicallycreated void within the interior region of the disc. Rather, accordingto aspects of the present invention, the prosthesis augments existing NPwithin the interior region of the vertebral disc rather than merelyreplace NP that was removed. In this manner, as will be explained,existing vertebral tissue may be displaced and a more naturalbiomechanical state is achieved, disc height is restored, and painresulting from impingement by the AF on nerve structures, loading offacet joints or pinching of the transverse nerve root due to reducedjoint space is minimized. A barrier may be employed to reduce thelikelihood of the prosthesis escaping from the interior region. Abarrier may also be employed to support the AF during and/or after theprosthesis is inserted.

[0068] In some instances, it may be desirable to monitor whether asufficient amount of prosthesis or prosthesis material 50 is placed intothe interior region 52 or whether the size of the prosthesis orprosthesis material 50 is sufficient to achieve the desired result, suchas, for example, restoring the functionality of the disc. Thus, in oneembodiment, certain disc characteristics are monitored during theimplantation procedure. In one embodiment, disc height (H) is monitoredsuch that the amount of prosthesis or prosthesis material 50 insertedinto the disc 15 is a function of the desired height (H) of the disc 15.As explained above, restoring disc height may be beneficial in reducingpain.

[0069] As will become clear hereinafter, it is to be appreciated thatthe prosthesis or prosthesis material implanted into the interior regionof the vertebral disc may have a predetermined geometry or may beinitially in bulk form allowing a surgeon or other technician to inserta desired amount of the prosthesis or prosthesis material into theinterior region of the disc. Thus, in embodiments where the prosthesisor prosthesis material is of a pre-formed geometry, the tern“prosthesis” may be used. In embodiments where the prosthesis orprosthesis material is a portion of a bulk material (such as when theprosthesis or prosthesis material is formed from a liquid or fluidmaterial) the phrase “prosthesis material” may be used. In bothembodiments, however, reference numeral “50” is used. Nevertheless, thepresent invention is not limited in this respect, as the term“prosthesis” may be used to refer to a portion of a bulk material andthe term “prosthesis material” may be used to refer to a pre-formedgeometry. As such, the term “prosthesis” is used herein to genericallyrefer to either embodiment.

[0070] Determining the height (H) may be performed using any suitablemeans or method, as the present invention is not limited in thisrespect. In one embodiment, a caliper or other measuring device todetermine the disc height may be used. Alternatively, disc height may bemonitored using any suitable imaging system, such as MRI, X-ray or CTScan, as the present invention is not limited in this respect. Further,such height data may be obtained either during the procedure orpost-operatively by, for example, comparing pre- and post-operative discheights. Once the desired disc height (H) is achieved, continuedinsertion of the prosthesis 50 into the interior region is terminated.The desired disc height (H) may be determined on a case by case basis.In one embodiment, the disc height (H) may be increased by an amountranging between approximately 1 mm and approximately 10 mm. Othersuitable ranges include 0.1 mm-5 mm and 5 mm-10 mm or even a narrowerrange, such as 0.1 mm-3 mm, 3 mm-6 mm and 6 mm-9 mm. It should beappreciated that the present invention is not limited to any particularresulting disc height (H), as other final disc heights or ranges may bedesired.

[0071] According to one aspect of the invention, increasing discpressure may be desirable to restore natural disc function. However,care should be taken so as not to exceed pressure limits of the disc.Studies have shown that pressures exceeding much more than 6 atmospheresmay damage the endplates of the vertebral disc. Therefore, instead of orin addition to monitoring the disc height, the pressure within disc 15may be monitored. That is, the amount of prosthesis material 50 insertedor the size of the prosthesis itself may be a function of an increase indisc pressure. In one embodiment, the amount of prosthesis implantedresults in an increase in pressure ranging from approximately 0.1atmospheres to approximately 5 atmospheres. It should be appreciatedhowever that the present invention is not limited in this respect andthat other suitable pressure ranges may be desirable. For example,pressure increases ranging from 0.1-2 atmospheres, 2-4 atmospheres oreven 4-6 atmospheres may be achieved.

[0072] Typically, the disc pressure is intradiscal pressure and thepressure is monitored while the disc 15 is in a resting state, e.g.,when there is no substantial axial force on the disc 15.

[0073] The disc pressure may be monitored using any suitable technique,as the present invention is not limited in this respect. As will bedescribed in greater detail, the actual pressure within the interiorregion of the disc may be monitored or it may be measured indirectly bymeasuring the force required to insert the prosthesis 50. That is, asthe prosthesis 50 is inserted into the interior region 52, the forceresisting the insertion may increase. Measuring or monitoring thisresistance force may indicate the internal pressure within the disc 15.

[0074] According to one aspect of the invention, increasing disc volumemay be desirable to restore natural disc function. Also, increasing discvolume may be employed as a method of indirectly increasing discpressure or disc height. Thus, in another illustrative embodiment, thevolume of the disc 15 may be monitored. Monitoring this characteristicmay be employed in combination with monitoring the disc pressure and/ormonitoring the disc height. Monitoring the disc volume may be achievedby CT scanning, X-ray imaging or MRI as the present invention is notlimited in this respect. Also, such monitoring may be performed bycomparing pre- and post-operative disc volumes.

[0075] Alternatively, the volume of prosthesis material 50 beinginserted into the interior region 52 may be measured directly bymonitoring the amount or size of the prosthesis itself. It should beappreciated that the present invention is not limited in this respect,as other suitable methods of monitoring disc or prosthesis volume may beemployed. The volume of the prosthesis material may also be adjusted tocompensate for extra swelling due to, for example, any existingherniations in the AF 17. For example, the volume of the prosthesismaterial 50 inserted into the interior region 52 may be increased toaccommodate such swelling.

[0076] A direct measurement of the amount of prosthesis material beinginserted may be employed, such as by the use of a metered dispensingimplement. Alternatively, because the volume of the prosthesis materialis a function of the specific dimensions of the vertebral disc, theprosthesis volume may be gathered from CT scan data, MRI data or othersimilar data from another imaging protocol. Thus, for example,prostheses with lesser volume can be used with smaller discs and thosewith limited herniation and those that otherwise require less NPdisplacement to increase disc height or intradiscal pressure.

[0077] In one illustrative embodiment, the volume of prosthesis material50 inserted into the interior region of the vertebral disc may rangebetween approximately 0.1 ml and approximately 6 ml. Other suitablevolume ranges, such as between approximately 1 ml and approximately 2 mlor between approximately 0.5 ml to approximately 2 ml, may be employed,as the present invention is not limited in this respect. The amount ofprosthesis material 50 implanted depends upon a number of factors,including the amount of vertebral tissue, such as NP, lost through anyherniation or degeneration and any increase in stiffness vertebraltissue, such as NP, as it is displaced with the prosthesis material.Further, the amount of prosthesis material inserted may depend upon theresulting augmentation volume of the vertebral disc desired.

[0078] Typical failure modes with existing vertebral disc implants maybe caused by placing the implant directly between two opposing endplateswhere the implant functions to resist compression. In this respect, themechanical properties of the prosthesis may create a stressconcentration along the endplates and fracturing of the endplates mayoccur. Furthermore, placing the prosthesis against both endplates mayinterfere with fluid and nutrient transfer in and out of the vertebraldisc. Thus, in one illustrative embodiment, as shown in FIGS. 1A and 1B,the prosthesis 50 is sized and shaped so as not to occupy the entirevolume of the interior region 52 of the vertebral disc. In anotherembodiment, as shown in FIG. 2, the prosthesis 50 is sized andpositioned within the interior region so as to be spaced from at leastone endplate 34. In another embodiment, the prosthesis 50 is sized so asto be spaced from both endplates 34, 36. In this manner, the prosthesis50 may be partially or wholly surrounded by NP material.

[0079] Upon insertion of the prosthesis 50 into the vertebral disc 15,displacement of the vertebral tissue occurs, such that the vertebraltissue is pushed and expands radially. For example, when the prosthesisdisplaces NP, the NP moves in opposite directions, i.e., towards theendplates 34, 36. The NP 20 cushions the prosthesis 50 and at least oneof the endplates 34, 36, and preferably both endplates, and allows for amore natural diffusion of fluids and nutrients. In the aboveembodiments, the prosthesis 50 is surrounded by NP; however, it need notbe. For example, in another embodiment, the prosthesis 50 is placed soas to lie adjacent the AF 17, as shown in FIG. 2.

[0080] The position of the prosthesis within the interior region of thevertebral disc may also be selected so as to alter the axis of rotationor reaction forces acting on a given functional spinal unit. Afunctional spinal unit moves with an axis of rotation that dictateswhich part of the functional spinal unit experiences the most motion orloading. The reaction force of the vertebral disc controls the axis ofrotation, therefore altering the reaction force location changes theaxis of rotation to reduce relative motion of parts of a functionalspinal unit. For example, as shown in FIGS. 3A and 3B, adding theprosthesis 50 to the posterior of vertebral disc 15 shifts the axis ofrotation closer to the facets 38, thereby reducing facet loading andfacet pain. Furthermore, positioning the prosthesis posteriorly has theeffect of increasing the disc height near the facets, which could alsohave the effect of reducing and relieving pain.

[0081] Other suitable positions for the prosthesis also may be employed.For example, as shown in FIG. 4, the prosthesis 50 may be positioned onone side of the vertebral disc 15 to restore symmetrical lateral heightand bending that may have been altered by disc degeneration or an AFdefect. A circumferential prosthesis 50, as shown in FIG. 5, or multipleprosthesis positioned about the circumference of the inner region (notshown) may also be employed. Other suitable combinations of positionsfor the prosthesis also may be employed to achieve other desiredresults.

[0082] Prosthesis 50 can be formed into any suitable shape. Prosthesis50 may be cube-like, spherical, disc-like, ellipsoid, rhombohedral,cylindrical, kidney, wedge, planar, or amorphous in shape as shown inFIGS. 6A and 6B. Further, a single prosthesis or prosthesis formed frommultiple sections or separate pieces may be employed. A plurality ofprostheses also may be employed and may be formed as beads, as shown inFIG. 8, substantially straight and/or spiral rods, as shown in FIG. 9,geometric solids, irregular solids, sheets or any other suitable shapedisclosed herein or otherwise formed. Of course, any suitablecombination of the above mentioned or other shapes may be employed.

[0083] In another embodiment, the prosthesis 50 is shaped to resistbeing extruded from the interior region of the vertebral disc 15. In oneexample, as shown in the illustrative embodiment of FIGS. 7A and 7B, theprosthesis 50 is sized to be larger than the access opening 60 formed inthe vertebral disc 15 for inserting the prosthesis 50. Alternatively, orin addition, the prosthesis may be formed as a wedge, as shown, with thelarger end of the wedge facing the opening 60 such that any forcetending to push the wedge out the access opening would cause theprosthesis to occlude the access opening, 60. Of course, the prosthesismay be shaped such that any axial loads on the prosthesis would tend tocause the prosthesis to move away from the access opening. For example,a wedge-shaped prosthesis with the smaller end facing the opening 60 mayrespond to axial loads by tending to move away from the opening.

[0084] To aid in healing of the disc or otherwise provide therapy, theprosthesis may be impregnated, coated or otherwise deliver varioustherapeutic agents, such as drugs, time-release drugs, genetic vectors,naked genes or the like to renew growth, reduce pain, aid healing, orreduce infection.

[0085] The prosthesis may be formed of any suitable material, as thepresent invention is not limitated in this respect. The prosthesis maybe formed as a fluid (e.g., liquid or gas), a solid, a gel, asemi-solid, or any suitable combination thereof. Exemplary fluidprostheses or prosthesis materials include, but are not limited to,various pharmaceuticals (steroids, antibiotics, tissue necrosis factoralpha or its antagonists, analgesics); growth factors, genes or genevectors in solution; biologic materials (hyaluronic acid,non-crosslinked collagen, fibrin, liquid fat or oils); syntheticpolymers (polyethylene glycol, liquid silicones, synthetic oils); andsaline.

[0086] In one illustrative embodiment, the prosthesis 50 is formed of abiocoinpatible material. Examples include biocompatible viscoelasticmaterials such as hydrophilic polymers, hydrogels, homopolymerhydrogels, copolymer hydrogels, multi-polymer hydrogels, orinterpenetrating hydrogels, acrylonitrile, acrylic acid, acrylimide,acrylimidine, including but not limited to PVA, PVP, PHEMA, PNVP,polyacrylamides, poly(ethylene oxide), polyvinyl alcohol,polyarylonitrile, and polyvinyl pyrrolidone, or combinations thereof. Itis preferred, but not required, that such materials may exhibitmechanical properties, swelling pressures and/or diffusion capabilitiessimilar to the natural NP in order to supplement the NP withoutcausing,g undo stress concentrations.

[0087] In other embodiments, the prosthesis 50 may be formed from solidmaterial, such as woven or non-woven materials or may include minuteparticles or even powder. The prosthesis 50 also may be porous orsemi-porous. Candidate materials include, but are not limited to:metals, such as titanium, stainless steels, nitinol, cobalt chrome;resorbable or non-resorbing synthetic polymers, such as polyurethane,polyester, PEEK, PET, FEP, PTFE, ePTFE, Teflon, PMMA, nylon, carbonfiber, Delrin, polyvinyl alcohol gels, polyglycolic acid, polyethyleneglycol; elastin; fibrin; ceramics, silicone, gel or rubber, vulcanizedrubber or other elastomers; gas filled vesicles, biologic materials suchas morselized or block bone, hydroxy apetite, collagen or cross-linkedcollagen, muscle tissue, fat, cellulose, keratin, cartilage, proteinpolymers, transplanted or bioengineered materials; variouspharmacologically active agents in solid form; or any combinationthereof. The solid or gel prosthesis materials may be rigid, wholly orpartially flexible, elastic or viscoelastic in nature. The prosthesismaterial may be hydrophilic or hydrophobic. Hydrophilic materials,mimicking the physiology of the NP, may be delivered into the disc in ahydrated or dehydrated state. Biologic materials may be autologous,allograft, zenograft, or bioengineered. Where rigid materials areemployed, the prosthesis may be shaped as small particles, powders,balls or spheres.

[0088] In some embodiments of the present invention, a multiphase systemmay be employed; for example, a combination of solids, fluids or gelsmay be used. Such materials may create primary and secondary levels offlexibility within an vertebral disc space. Thus, in use, the spine willflex easily at first as the vertebral disc pressure increases and thefluid flows, loading the annulus. Then, as the disc height decreasesflexibility may decrease. This combination may also prevent damage tothe AF under excessive loading as the prosthesis may be designed toresist further compression such that further pressure on the AF islimited.

[0089] Any of a variety of additional additives such as thickeningagents, carriers, polymerization initiators or inhibitors may also beincluded, depending upon the desired infusion and long-term performancecharacteristics. In general, “fluid” is used herein to include anymaterial which is sufficiently flowable at least during the infusion(i.e., implantation) process, to be infused by a delivery device intothe interior region of the vertebral disc. The prosthesis material mayremain “fluid” after the infusion step, or may polymerize, cure, orotherwise harden to a less flowable or nonflowable state.

[0090] In one embodiment, in situ polymerizing prosthesis materials thatare well-known in the art and are described in U.S. Pat. No. 6,187,048,incorporated herein by reference, may be used. Phase changingaugmentation preferably changes from a liquid to a solid or gel. Suchmaterials may change phases in response to contact with air, increasesor decreases in temperature, contact with biologic liquids or by themixture of separate reactive constituents. These materials may bedelivered through an opening in the AF or down a tube or cannula placedpercutaneously into the disc. Once the materials have solidified orgelled, they may exhibit the previously described characteristics of asolid prosthesis material.

[0091] Additional additives and components of the prosthesis materialare recited below. In general, the nature of the material may remainconstant during the deployment and post-deployment stages or may change,from a first infusion state to a second, subsequent implanted state. Forexample, any of a variety of materials may desirably be infused using acarrier such as a solvent or fluid medium with a dispersion therein. Thesolvent or liquid carrier may be absorbed by the body or otherwisedissipate from the disc space post-implantation, leaving the materialbehind. For example, any of a variety of the powders identified belowmay be carried using a fluid carrier. In addition, hydrogels or othermaterials may be implanted or deployed while in solution, with thesolvent dissipating post-deployment to leave the hydrogel or other mediabehind. In this type of application, as discussed above, the disc spacemay be filled under higher than ultimately desired pressure, taking intoaccount the absorption of a carrier volume.

[0092] In one embodiment, the prosthesis material comprises a materialhaving a compressive strength that is less than approximately 4 MN/m².In another embodiment, the prosthesis material has a compressivestrength of approximately 2.5 MN/m² to approximately 3.5 MN/m². Othersuitable prosthesis materials having compressive strengths less than orequal to approximately 2.5 MN/m² or approximately 3.5 MN/m² toapproximately 4 MN/m² may be employed.

[0093] In addition, the prosthesis material may have a Poisson's ratiothat is between approximately 0.30 and approximately 0.49. Such aPoisson's ratio may be employed to effectively distribute the loadoutward toward the AF. In one embodiment, the Poisson's ratio is betweena range of approximately 0.35 and approximately 0.49. Rubber andpolymeric materials may be used or otherwise formed to produce thedesired Poisson ratio. In one embodiment, a hydrogel, such as PVA, PGAor PMMA, may be used.

[0094] As discussed above, it may be desirable to provide a prosthesismaterial that mimics as closely as possible the NP within the interiorregion of the vertebral disc. Thus, the prosthesis may be formed of amaterial that absorbs and/or releases fluids within a certain period oftime and under certain conditions similar to the absorption and releaseof fluids from the natural NP. Upon high axial loads of the vertebraldisc, the prosthesis may release fluids to help diffuse shock loading.Similarly, the ability for the prosthesis to absorb fluid should besufficiently rapid so as to rebulk when fluid is otherwise released fromthe prosthesis. In one embodiment, it may be desirable for theprosthesis to absorb fluids during a 5 to 10 hour sleep cycle so as torestore any fluid loss during the day. In one embodiment, the prosthesisis formed of a material that may enable it to absorb approximately 50%to 100% of its volume. However, the present invention is not limited inthis respect and other suitable prosthesis materials or characteristicsof a prosthesis material may be employed to achieve other rehydrationvolumes. Rubber and polymeric materials may be used. In one embodiment,a hydrogel, such as PVA, PGA or PMMA, may be used.

[0095] In one embodiment, the prosthesis material has a swellingpressure between approximately 1 MN/m² and approximately 9 MN/m² forgiven volume range between approximately 0.1 mL and 6.0 mL. This mayhave the advantage of allowing a smaller prosthesis to swell and fitinto the irregularities within the natural NP until equilibrium pressureis achieved. Rubber and polymeric materials may be used. In oneembodiment, a hydrogel, such as PVA, PGA or PMMA, may be used.

[0096] In one embodiment, the prosthesis material may be formed as ahydrogel having a compressive strength ranging between approximately 2.5MN/m² and approximately 3.5 MN/m². In addition, the prosthesis materialmay preferably have a swelling characteristics that enables it torehydrate approximately 50% to 100% of its volume within a 1 hour to 8hour time period under a compressive stress ranging from approximately0.2 MN/m² and approximately 0.8 MN/m². Further, the prosthesis materialmay hydrate in less time when in an unloaded or unconstrainedenvironment. Further, in this embodiment, the prosthesis material mayhave a Poisson's ratio ranging from approximately 0.35 to approximately0.49 under a compressive stress ranging from approximately 0.5MN/m² toapproximately 2 MN/m². Rubber and polymeric materials may be used. Inone embodiment, a hydrogel, such as PVA, PGA or PMMA, may be used.

[0097] In some embodiments it may be desirable to provide a more uniformloading at the junction between the prosthesis material and the NP, AFor endplates to reduce stress concentration and limit damage to any ofthe foregoing. Thus, in one embodiment, the prosthesis material may be arelatively soft and flexible material. In addition, in one embodiment,the prosthesis material may be isotropic. Rubber and polymeric materialsmay be used. In one embodiment, a hydrogel, such as PVA, PGA or PMMA,may be used.

[0098] In one embodiment, the prosthesis is a biocompatible isotropichydrogel, such as PVA, PGA or PMMA, having a compressive strength ofless than 4 MN/m².

[0099] In some instances it may be desirable to remove the prosthesismaterial from the interior region of the vertebral disc. Thus, in oneembodiment, the prosthesis is sized, shaped or otherwise configured soas to be relatively easily removed after having been implanted. In oneembodiment, this result may be achieved by selecting the shape of theprosthesis and/or the rigidity or deformability of the material.

[0100] The prosthesis implanted into the interior region of the disc mayalso be used in conjunction with a barrier that blocks, covers orotherwise occludes the access opening, whether it be surgically createdor a hernia site. After the prosthesis 50 is inserted into the interiorregion, a barrier 70 (see FIG. 10), such as that disclosed in applicantscommonly assigned patents and patent application, including U.S.application Ser. No. 10/055,504, U.S. Pat. No. 6,425,919 and 6,508,839,each of which is hereby incorporated by reference, is inserted. Ofcourse, other suitable barriers or no barrier may be employed.

[0101] As shown in FIG. 10, and as described in one or more of theabove-mentioned patents or application, the barrier 70, if used, may besized to sufficiently cover the defect or access opining 60 and reducethe likelihood of the barrier 70 extruding or slipping from covering theaccess opening 60. The barrier 70 may be sized, such that at least someportion of the barrier abuts the AF surrounding the access opening 60.The barrier 70 may act to seal the opening 60, recreating the closedisobaric environment of a healthy disc. The barrier 70 also may beaffixed to tissues within the functional spinal unit or to the AFsurrounding the opening 60. Such attachment may be facilitated with theuse of sutures, staples, glues or other suitable fixation means orfixation devices.

[0102] In use, the pressurized disc tissue and prosthesis 50 appliesforce on the inwardly facing surface of the barrier 70. This pressuremay be exploited by the design of the barrier to reduce the likelihoodof it dislodging or moving from its intended position. One exemplarybarrier is shown in FIG. 11, where the barrier 70 includes inwardlyfacing surfaces 72 that expand upon the application of pressure. As thebarrier expands, it becomes less likely to be expelled from the disc.The barrier 70 may be formed with a concavity facing inwardly to promotesuch expansion. In addition, as shown in FIG. 10, the prosthesismaterial 50 typically is positioned adjacent to the barrier 70 such thatthe likelihood of natural NP escaping through the access opening 60 isfurther minimized.

[0103] The barrier may be flexible in nature. It can be constructed of awoven material such as Dacron or Nylon, a synthetic polyamide orpolyester, a polyethylene, or can be an expanded material, such asexpanded polytetrafluroethylene (e-PTFF). The barrier may also be abiologic material such as cross-linked collagen or cellulous.

[0104] The barrier typically is a single piece of material, and may beexpandable or include a component that allows it to be expanded from acompressed state after insertion into the interior of the disc. Thisexpansion may be active, such as a balloon, or passive, such as ahydrophilic material. The expansion may also occur via a self-expandingdeforming barrier or by incorporating such a material, such as ashape-memory material, for example. In the example shown in FIG. 11, thebarrier 70 includes a cage 74 formed from a shape-memory material, suchas nitinol. A cover (not shown) may be employed over the cage 74.

[0105] When a phase changing prosthesis material is used, the barrier orother annulus augmentation may be permanently implanted or used onlytemporarily until the desired phase change has occurred. For example, asufficient amount of fluid or liquid prosthesis 50 may be implanted intothe disc. Barrier 70 is then implanted to occlude the access opening 60.The prosthesis 50 is then cured or dried (or otherwise allowed to cureor dry) to a solid or semi-solid state, wherein the resulting prosthesisform is larger than the access opening. The barrier 70 then may beremoved, as, due to the resulting size and/or shape of the prosthesis,the likelihood of the prosthesis escaping back through the accessopening 60 is low.

[0106] As discussed above, the prosthesis 50 typically is placed withinthe interior region 52 of the vertebral disc 15 by a delivery device.Examples of suitable delivery devices are shown in FIGS. 12-22 In oneillustrative embodiment, the delivery device 80 comprises a body 82defining a longitudinal axis 83. The body 82 may be formed as anelongate cannula or other hollow tubular sleeve. The body 82 includes aproximal end 81 and a distal end 84, which is adapted to pass throughthe access opening 60 in the AF and deploy the prosthesis 50 into theinterior region 52. The distal end 84 may be rounded (not shown) tolimit any damage to the AF or other anatomical structure. A push rod orplunger 86 is axially slidable within the cannula 82 and together withthe end portion 84 of the cannula defines a holder region 87. Theplunger 86 includes an end 89 that acts on the prosthesis 50 to dislodgethe prosthesis from the holder region 87. The plunger 86 is pushed inthe direction of arrow A shown in FIG. 12B to eject the prosthesis 50from the holder region 87.

[0107] The plunger is axially slidable within the body so as to dislodgethe prosthesis material therefrom. As shown for example in FIGS.12A-12C, in one embodiment, the body 82 includes a first handle 160 orregion to allow the surgeon to grasp the outside of the body. Theplunger 86 includes a second handle 162, allowing the surgeon to actuatethe plunger 86 to dislodge the prosthesis material 50.

[0108] The prosthesis material 50 may be inserted into the holder region87 of the deployment device 80 using any suitable means. In this manner,a single use deployment device may be provided. In one embodiment, thedeployment device may be preloaded with a desired amount of prosthesismaterial. In other embodiments, the deployment device may be placed in avat of prosthesis material and actuated, in a manner similar to asyringe, to draw the prosthesis material into the deployment device.Alternatively, a surgeon or other assistant may place a desired amountof the prosthesis material within the deployment device. Of course, itshould be appreciated that the present invention is not limited in thisrespect and that any suitable means or method for inserting theprosthesis may be used. And, the chosen means or method may depend uponthe type of prosthesis material employed.

[0109] In one embodiment, any of the deployment devices and/or theprosthesis described herein may be supplied in a kit. The kit mayinclude one or more of the same or different prostheses or componentsand/or one or more of the same or different deployment devices. The kitmay include materials or devices to be used with the prosthesis. Forexample, the kit may include the above-mentioned therapeutic agents oragents to cure the prosthesis, if a curable prosthesis is employed.Also, the kit may include components, devices or other materials to aidin deploying the prosthesis. The kit further may include one or more ofthe same or different barriers. The kit also may include monitoringdevices to monitor the amount of prosthesis being deployed and also mayinclude instructional information, including any of the methodologiesdescribed herein. It should be appreciated that the present invention isnot limited in this respect, as the herein noted or other suitablecomponents or devices may be supplied with the kit.

[0110] In some instances, it may be desirable to locate the prosthesismaterial within a certain position in the interior region of thevertebral disc. Thus, in one illustrative embodiment as shown in FIGS.12A-12C, the deployment device includes a depth stop 88 that limits howdeeply into the interior region of the vertebral disc the prosthesis isplaced. For example, the depth stop 88 may seat against the vertebralbodies 28, 30, as shown in FIG. 12C, or the AF 17. In this manner, thetip 84 of the delivery device 80 is inserted into the access opening 60in the AF until the depth stop 88 contacts the outer layer of the AF toprevent further insertion of the tip of the delivery device into theinterior region of the vertebral disc. Once in this position, thedelivery device is actuated to deliver the prosthesis 50 to the desiredlocation. Although in this embodiment the depth stop 88 abuts thevertebral body to limit the insertion depth, the delivery device may beconfigured such that the depth stop abuts other anatomical features. Forexample, the depth stop may be located on a delivery device such that itis adapted to contact the AF or other bone or tissue located in theregion.

[0111] In the embodiment shown in FIGS. 12A-12C, the depth stop 88 islocated on the outside of the delivery device. However, in otherembodiments, an example of which is shown in FIG. 13, it may bedesirable to configure the delivery device 80 with an internal depthstop 90. In this manner, the tip of the delivery device is placedthrough the access opening in the AF and is advanced until the internaldepth stop 90 contacts the opposite wall of the AF or other structurewithin the interior region of the vertebral disc. Once the tip is in theproper position, the delivery device is actuated to deploy theprosthesis material at the suitable location within the interior regionof the vertebral disc.

[0112] The depth stop also may be adjustable, giving the surgeon theflexibility to locate the prosthesis in any desired position. In oneexample, as shown in FIG. 14A, the body 82 may include a threadedsection 92 and a depth stop 88′ may be formed as a threaded ring 94 thatengages the body 82. By rotating the ring 94 relative to the body, thelocation of the depth stop may be adjusted.

[0113] Although a thread is shown and described, other suitableadjustment mechanisms may be employed. For example, as shown in FIGS.14B and 14C, a depth stop may be slidingly engaged on the body 82 andlocked in a position using a suitable locking device, such as a clamp orthumb-screw 96 for a depth stop 88″ shown in FIG. 14B, ball 98 anddetent 99 mechanism for a depth stop 88′″ shown in FIG. 14C, or otherratcheting-type mechanisms.

[0114] In another embodiment, as shown in FIG. 14D a depth stop 88″″ isformed as a plurality of washer-like rings 100 that can slip over thebody and abut a fixed depth stop 102. In this manner, the depth may beset by adding rings onto the body until the desired depth is achieved.The rings may be locked in position or freely retained on the body.

[0115] An internal depth stop may be adjustable providing the desiredflexibility as to where to locate the prosthesis. One example is shownin FIG. 15, in which a depth stop 90′ is threaded into a wall of thebody 82 to enable depth adjustment in a telescoping manner.

[0116] To further enhance placement of the prosthesis in a desiredlocation within the interior of the vertebral disc, the delivery device80 may include a curved or otherwise articuatable end 84 that can beeither actively or passively manipulated to alter its position, as shownin FIG. 16. With a deployment device having a straight end as shown, forexample, in FIG. 12A, the prosthesis may only be deployed along thelongitudinal axis of the delivery device. In embodiments employing acurved or articuatable end, the prosthesis may be deployed at anydesired angle relative to the longitudinal axis. For example, theprosthesis may be deployed adjacent one of the endplates, in the middleof the interior region of the vertebral disc, or adjacent the AF.

[0117] One illustrative embodiment of an articulatable end is shown inFIG. 16. Guide wires 110 are fixed to the tip 84 of the delivery device,and in one embodiment, the guide wires 110 are anchored using suitableanchors, such as eyelets, in the interior region of the body 82. Thewires 110 extend internally through body 82 toward the proximal end 81of the body 82 and exit end 81. Retracting the wires 110 causes the tip84 to articulate relative to the longitudinal axis of the deliverydevice. Other mechanisms for causing the tip to curve or bend may beemployed. To provide for an articulating end, the distal end 84 isformed of a flexible material or in a flexible configuration.

[0118] In another embodiment, rather than actively deforming the tip ofthe delivery device, the tip itself may be configured such that it bendsinto a predetermined configuration upon insertion. For example, the tipof the delivery device may include a kink point or a change in thestiffness along the length of the tip that causes the tip to assume apredetermined configuration. In one embodiment, as shown in FIG. 17, thedelivery device 80 includes a relatively stiff outer tubular member 112that contains the body 82. Further, body 82 may be formed of, orotherwise include, a relatively flexible material, such as a springmember, that holds the tip in a bent configuration. When inside thesleeve 112, the tip is retained in a, straight configuration to allowinsertion into the vertebral disc. When body 82 is displaced withrespect to member 112 in the direction of arrow B, the tip 84 emergesfrom the sleeve 112 and assumes its bent configuration, as shown.

[0119] When a curved or otherwise articuatable end is employed, plunger86 should be sufficiently flexible to conform to the shape of the tip ofthe delivery device when in its bent configuration so as to be able todislodge the prosthesis material.

[0120] In some circumstances, it may be desirable to place theprosthesis at a desired location within the interior region of thevertebral disc upon retracting a portion of the delivery device ratherthan by extruding the prosthesis material from the delivery device 80,as in the embodiment shown in FIGS. 12A-12C. Thus, in this embodimentshown in FIGS. 18A-18C, and FIG. 19, a retrograde delivery device 80 isshown, wherein the body 82 is retracted in the direction of arrow C (seeFIG. 18B) relative to the plunger 86. Once the prosthesis material hasbeen deployed within the interior region, the delivery device may beremoved from the vertebral disc.

[0121] The delivery device of this embodiment may also include a curvedor articulatable end as described above and/or a depth stop, whether ornot adjustable, to place the prosthesis at the desired location.

[0122] As shown in FIGS. 18A-18C, the delivery device may include adepth stop 88. To provide the depth stop 88 while allowing the body tobe retracted along arrow C as described, the body includes a slot 120,as shown in FIG. 19. Thus, the tip 84 of the delivery device is insertedinto the interior region of the vertebral disc until the depth stop 88contacts the desired anatomy. Then, the body 82 may be retracted alongarrow C while the depth stop 88 is held against the anatomy. The slot120 in the body 82 allows the body 82 to be retracted such that the stop88 may move relative to the body 82 within the slot 120.

[0123] As discussed above, the prosthesis may be formed of any suitablematerial including solids, semi-solids or even materials in liquid orfluid form. However, injecting a fluid or liquid prosthesis material mayincrease the risk of adding localized pressure as the fluid works itsway through the interior region of the vertebral disc, which may resultin damage to the disc. In addition, merely injecting the fluid into theinterior region can result in imprecise placement within the interiorregion or possibly inadvertently deliver the material into undesiredlocations, such as near the endplates or at fissures or tears in the AF,all potentially increasing the likelihood of pain or reducing theeffectiveness of the prosthesis.

[0124] In one embodiment as shown in FIG. 20A, the delivery device 80 isadapted to deliver a prosthesis that is in fluid or liquid form. In thisembodiment, end 84′ is generally closed, but includes perforations 132and the prosthesis is held within holder region 87. Upon advancing theplunger 86, the liquid or fluid prosthesis material within the holder 87is extruded, ejected or otherwise dispensed through the perforations 132in the direction of arrow D.

[0125] The perforations formed in the tip may be any suitableperforations including holes, as shown, or other openings.Alternatively, as shown in FIG. 20B, the perforations may be in the formof fins 132′ that direct the liquid or fluid prosthesis material in thedirection of arrow D′. In one embodiment, the delivery device includesperforations extending only radially outwardly. In this manner, directpressure through the end of the delivery device onto the NP or locatingthe prosthesis in an otherwise undesirable location may be avoided.

[0126] In another embodiment, the deployment device monitors the amountof material being delivered. In one illustrative embodiment as shown inFIGS. 21A-21B and 20, the delivery device 80 includes a gauge 140 suchthat the surgeon, for example, may quickly determine the amount ofprosthesis material being deployed from the delivery device. In oneembodiment, the gauge 140 may be a pressure gauge that may be used todetermine the increase in pressure within the vertebral disc as theprosthesis material is being deployed. In one embodiment as shown inFIG. 21A, the gauge may include a pressure sensitive transducer 142disposed on or within the plunger 86 and suitable electronics (notshown) to record and measure the pressure within the disc. The pressuretransducer may be situated on the delivery device such that it recordsthe resistance to insertion force. The resistance force is correlated tothe pressure increase within the vertebral disc such that the surgeonwould know when enough prosthesis material has been deployed. Thepressure also may be determined with the use of a suitably placed straingauge.

[0127] Alternatively, the gauge may be a mechanical gauge 144 As shownin FIG. 21B, that employs a spring 146 and an indicator 148 coupled tothe spring that moves in response to the resistance to insertion force.Again, the resistance force may be correlated to the increase inpressure in the interior region of the disc such that when a certainresistance force is obtained, further insertion of prosthesis materialmay be terminated. In this embodiment, the plunger 149 is formed as atwo-part plunger having a first plunger 149A and a second plunger 149B.Spring 146 is disposed between the two plungers. Moving plunger 149Acauses spring 146 to compress and act on plunger 149B, which in turndislodges prosthesis 50. As the resistance to insertion increases,plunger 149A moves further into plunger 149B and a higher pressurereading is indicated at indicator 148. It should be appreciated that thepresent invention is not limited to any particular gauge as any suitablegauge may be employed to determine the increase in pressure in theinterior region of the vertebral disc.

[0128] In another embodiment as shown in FIG. 22, the gauge may be avolume gauge 150 to indicate the volume of prosthesis material beingdelivered to the interior region of the vertebral disc. In this respect,the delivery device may be configured similar to a syringe and includesa series of lines on the body that correlates to the volume of materialbeing deployed.

[0129] In yet another embodiment (not shown), a combination of gaugesmay be employed. For example, a deployment including both a pressuregauge (such as pressure transducer 142) and a volume gauge (such asindicator 150) may me employed.

[0130] The delivery device 80 may be formed from any suitable material,as the present invention is not limited in this respect. Thus, thedelivery device may be formed from a plastic material, such as apolycarbonate, or a metal material, such as stainless steel, or anysuitable combination of materials. In addition, the delivery device maybe formed of a material that can be readily sterilized. Further, thedelivery device may be formed as a single use device such thatresterilization is not required after use.

[0131] In another embodiment, in addition to the shapes described above,the prosthesis may include a grouping of multiple components of the sameor different shapes that can be inserted into the interior region of thevertebral disc as a group. By grouping smaller discrete componentprostheses together, the prosthesis may perform differently than asingle unit which can be advantageous. The volume of an individualcomponent prosthesis can range between approximately 10 mm³ andapproximately 500 mm³. Each component of the group, or at least onecomponent, may be formed of the same or different materials or materialcharacteristics as other components of the group, such as thosematerials or characteristics described herein, as the present inventionis not limited in this respect.

[0132] The delivery device 80 may deploy the grouping of prosthesiscomponents of any desired shape. When delivering a grouping ofcomponents, each (or at least one) prosthesis component may be in theform of spheres or beads (see FIG. 8), rods or spirals (see FIG. 9),geometric solids, irregular solids, sheets or any other suitable shapedisclosed herein or otherwise formed. The components typically aredeployed in a group and in a single step. At least one componentprosthesis from the group, or the entire group, may be deployed to anydesired location, examples of which are discussed above. In oneembodiment, the grouping includes at least two components forming theprosthesis. In another embodiment, the grouping includes at least threecomponents forming the prosthesis. Other suitable grouping sizes, suchas four, five and six, may be employed, as the present invention is notlimited in this respect. In one embodiment, the multi-componentprosthesis can, for example, comprise hydrogel spheres, that can beextruded, ejected or otherwise dispensed from the delivery device,thereby displacing, without removing, autologous vertebral tissues. Asis apparent from the above discussion, the size of the group may dependupon certain factors. For example, as is apparent from the abovediscussion, the group size may be a function of the desired disc height,the desired disc pressure or the desired disc volume, such as thedesired augmentation volume.

[0133]FIG. 23A is a cross-sectional view of a delivery device 80 loadedwith a grouping of spherical or bead shaped prosthetic components 50′and with the plunger 86 in the retracted position. FIG. 23B shows theplunger 86 in the advanced position, with the components 50′ of theprosthesis deployed as a group from the distal tip 84. FIG. 23C shows aview of two adjacent vertebral bodies 28, 30, with the tip 84 of thedelivery device 80 inserted within the vertebral disc. Depth stop 88 isplaced against at least a portion of the annulus or vertebral body. Theplunger 86 is shown in the advanced position in which the prosthesis 50′has been delivered within the area bounded by the annulus, causing thetissues of the annulus, nucleus, or vertebral endplates to be displacedin relation to the amount of prosthesis added.

[0134]FIG. 24A is a cross-sectional view of a retrograde delivery device(such as that described above with respect to FIGS. 18A-18C), which isloaded with rod- or spiral-shaped prosthetic components 50″ and with thebody 82 advanced relative to the plunger 86. FIG. 24B shows the body 82in the retracted position relative to the plunger 86, in which thecomponents 50″ of the prosthesis are deployed as a grouping from thedistal tip 84. FIG. 24C shows a view of two adjacent vertebral bodies28, 30, with the tip 84 delivery device 80 inserted within the vertebraldisc. Depth stop 88 is placed against at least a portion of the annulusor vertebral body. The body 82 of the delivery device is shown in theretracted position relative to the plunger 86, with the prosthesis 50delivered within the area bounded by the annulus, causing the tissues ofthe annulus, nucleus, or vertebral endplates to be displaced in relationto the amount of prosthesis added.

[0135] Although the spherical- or bead-shaped prosthesis 50′ is shown inthe delivery device of FIGS. 23A-23C and the rod- or spiral-shapedprosthesis 50″ is shown in the delivery device of FIGS. 24A-24C, thepresent invention is not limited in this respect. Thus, the spherical-or bead-shaped prosthesis 50′ may be deployed with any delivery devicedescribed herein or otherwise, including the delivery device shown inFIGS. 24A-24C and the rod- or spiral-shaped prosthesis 50′ may bedeployed with any delivery device described herein or otherwise,including the delivery device shown in FIGS. 23A-23C.

[0136] It should be understood that the foregoing description of theinvention is intended merely to be illustrative thereof and that otherembodiments, modifications, and equivalents of the invention are withinthe scope of the invention recited in the claims appended hereto.Further, although each embodiment described above includes certainfeatures, the invention is not limited in this respect. Thus, one ormore of the above-described or other features of the prosthesis, methodof implantation, or delivery device, may be employed singularly or inany suitable combination, as the present invention is not limited to aspecific embodiment.

What is claimed is:
 1. A vertebral disc prosthesis for displacingnucleus, annulus, or vertebral body endplate tissue of a vertebral disc,the prosthesis comprising: a grouping of at least two discretecomponents, the grouping constructed and configured to be insertedtogether as a group into the interior region of a vertebral disc todisplace at least a portion of the nucleus, annulus, or vertebral bodyendplate tissue.
 2. The prosthesis according to claim 1, wherein eachcomponent is formed of a mass of material having a compressive strengthof less than 4 MN/m².
 3. The prosthesis according to claim 1, wherein atleast one component comprises a hydrogel material.
 4. The prosthesisaccording to claim 1, wherein at least one component is isotropic. 5.The prosthesis according to claim 1, wherein at least one component isconstructed to selectively absorb or release fluid.
 6. The prosthesisaccording to claim 1, wherein at least one component comprises aviscoelastic material.
 7. The prosthesis according to claim 1, whereinat least one component comprises a spherical shape.
 8. The prosthesisaccording to claim 1, wherein at least one component comprises a rod orspiral shape.
 9. The prosthesis according to claim 1, wherein at leastone component comprises a therapeutic amount of a desired substance andis constructed to deliver the therapeutic amount of the desiredsubstance to the vertebral disc.
 10. The prosthesis according to claim1, wherein at least one component comprises a Poisson's ratio between arange of approximately 0.30 and approximately 0.49.
 11. The prosthesisaccording to claim 1, wherein at least one component has a compressivestrength between a range of approximately 2.5 MN/m² and approximately3.5 MN/m².
 12. The prosthesis according to claim 1, wherein at least onecomponent is adapted to absorb approximately 50% to approximately 100%of its volume within approximately 1 hour to approximately 8 hours undera compressive stress between a range of approximately 0.2 MN/m² and 0.8MN/m².
 13. The prosthesis according to claim 1, in combination with abarrier that is constructed to cover an opening in the annulus of thevertebral disc.
 14. The prosthesis according to claim 1, wherein thegrouping comprises at least three discrete components.
 15. A method ofrestoring function of an vertebral disc, the vertebral disc havingvertebral disc tissue comprising a nucleus, an annulus, and vertebralbody endplate tissue, the method comprising: locating an access site onthe vertebral disc; and inserting, at one time, a prosthesis comprisinga grouping of at least two discrete components through the access siteand into an interior region of the vertebral disc to displace at least aportion of the vertebral disc tissue without removing a substantialamount of nucleus tissue.
 16. The method according to claim 15, whereinlocating an access site comprises forming an opening in the annulustissue.
 17. The method according to claim 15, wherein locating an accesssite comprises locating a defect in the annulus tissue.
 18. The methodaccording to claim 15, wherein inserting the grouping of componentprostheses into the interior region of the vertebral disc comprisesinserting at least one grouping of component prostheses into theinterior region of the vertebral disc that is of a sufficient size toachieve a desired disc height.
 19. The method according to claim 15,wherein inserting the grouping of component prostheses into the interiorregion of the vertebral disc comprises inserting at least one groupingof component prostheses into the interior region of the vertebral discthat is of a sufficient size to achieve a desired augmentation volume.20. The method according to claim 15, wherein inserting the grouping ofcomponent prostheses into the interior region of the vertebral disccomprises inserting at least one grouping of component prostheses intothe interior region of the vertebral disc that is of a sufficient sizeto achieve a desired disc pressure.
 21. The method according to claim15, wherein inserting the grouping of component prostheses into theinterior region of the vertebral disc comprises inserting a grouping ofcomponent prostheses, with at least one component prosthesis beingformed of a hydrogel material.
 22. The method according to claim 15,wherein inserting the grouping of component prostheses into the interiorregion of the vertebral disc comprises inserting a grouping of componentprostheses, with at least one component prosthesis being formed as anisotropic mass of material.
 23. The method according to claim 15,further comprising forming at least one component prosthesis with atherapeutic amount of a desired substance.
 24. The method according toclaim 15, wherein further comprising forming at least one componentprosthesis so as to exhibit a compressive strength that is less than 4MN/m².
 25. The method according to claim 15, further comprisinginserting a barrier into the vertebral disc so as to cover an opening inthe annulus tissue.
 26. The method according to claim 15, furthercomprising locating the grouping of component prostheses within theinterior region of the vertebral disc so as to be surrounded by nucleustissue within the interior region of the vertebral disc.
 27. The methodaccording to claim 15, wherein inserting a grouping of componentprostheses into the interior region of the disc comprises inserting agrouping of component prostheses having at least one componentprosthesis shaped substantially as a sphere.
 28. The method according toclaim 15, wherein inserting a grouping of component prostheses into theinterior region of the disc comprises inserting a grouping of componentprostheses having at least one component prosthesis shaped substantiallyas a rod or spiral.